Fast cure epoxy resin systems

Abstract

A fast cure epoxy resin system is provided that upon curing has a Tg no greater than 140° C. and a Phase angle below 20° at a temperature of 140° C. or below, and prepregs and mouldings based on the system. The resin formulation matches the reactivity of the resin to the amount of curative and hardener employed.

1 . An epoxy resin formulation containing a curative, the formulation being curable at 150° C. in no more than 150 seconds, and being curable at 120° C. in no more than 4 minutes to provide a cured resin having Tg no greater than 140° C. 
     
     
         2 . An epoxy resin formulation according to  claim 1  having a Phase angle when cured of below 20″ at a temperature below 140° C. 
     
     
         3 . An epoxy resin according to  claim 2  in which the Phase angle is below 15°. 
     
     
         4 . An epoxy resin formulation according to  claim 1  comprising from 4 to 10 wt % based on the weight of the epoxy resin of one or more urea based curing agents. 
     
     
         5 . An epoxy resin formulation according to  claim 1  comprising from 7% to 10% of a hardener. 
     
     
         6 . An epoxy resin formulation according to  claim 5  in which the hardener is dicyandiamide. 
     
     
         7 . An epoxy resin formulation according to  claim 2  in which the epoxy resin has a functionality of at least 2. 
     
     
         8 . An epoxy resin formulation according to  claim 1  in which the epoxy resin has a storage modulus G′ of from 3×10 5  Pa to 1×10 8  Pa and a loss modulus G″ of from 2×10 6  Pa to 1×10 8  Pa at a temperature of 20° C. 
     
     
         9 . An epoxy resin formulation according to  claim 1  in which the epoxy resin has a complex viscosity of from 5×10 5  Pa to 1×10 7  Pa·s at a temperature of 20° C. 
     
     
         10 . A prepreg comprising fibrous reinforcement and an epoxy resin formulation according to  claim 1 . 
     
     
         11 . A prepreg according to  claim 10  in which the resin content by volume of the uncured prepreg is in the range of from 15 to 70% by volume of the prepreg. 
     
     
         12 . A prepreg according to  claim 10  in which the fibrous reinforcement comprises cracked, selectively discontinuous or continuous filaments. 
     
     
         13 . A prepreg according to  claim 10  in which the filaments. are made from carbon, basaltic fibre, graphite, glass, metalized polymers, aramid, natural fibres and/or mixtures thereof. 
     
     
         14 . A process for the production of laminar structures by laying up a stack of layers of prepregs according to  claim 10  and causing the stack to cure. 
     
     
         15 . A stack of prepregs containing an epoxy resin of functionality at least 2 and an EEW from 150 to 1500 and containing a curative the resin being curable by an externally applied temperature at 150° C. in no more than 150 seconds to provide a cured resin haying a Tg no greater than 140° C., 
     
     
         16 . A stack of prepregs according to  claim 15  in which the epoxy resin formulation has a Phase angle when cured of less than 20° at temperatures of 140° C. or below. 
     
     
         17 . A laminar structure comprising a cured stack of prepregs according to  claim 15 .